1. Field of the Invention
The present invention relates to an optical pickup unit, an apparatus for recording/reproducing data, a control method, and a recording medium, and more particularly to an optical pickup unit, and a recording/reproducing apparatus which use a near-field, a control method for effectively using the optical pickup unit and the recording/reproducing apparatus, and a recording medium for use in the same.
2. Discussion of the Related Art
Generally, an optical recording/reproducing device has been used to record/reproduce data in/from a recording medium (e.g., a compact disc (CD) or a digital versatile disc (DVD)).
As consumer's taste grows, a technique for processing the high-quality moving images is required by consumers. As a moving-image compression technology grows, high-density recording mediums are also required by the consumers.
A representative technology from among a variety of kernel technologies for developing the high-density recording medium is a technology associated with an optical pickup unit.
A recording density of the above-mentioned recording medium is influenced by a diameter of an optical signal illuminated on a record layer of the recording medium. In other words, the lower the diameter of the optical signal focused on the recording medium, the higher the recording density.
In this case, the diameter of the focused optical signal is mainly determined by two factors. One factor is a Numeric Aperture (NA) indicating a throughput of the lens used to focus the optical signal, and the other factor is a wavelength of the optical signal focused on the lens.
The shorter the wavelength of the focused optical signal, the higher the recording density. Therefore, a short-wavelength optical signal is used to increase the recording density. If a blue-colored optical signal is used instead of a red-colored optical signal, the recording density becomes higher.
However, a far-field recording system's head employing a general lens has a limitation in diffracting the optical signal, so that there is a limitation in decreasing the diameter of the optical signal.
In order to solve the above-mentioned problems, many developers are conducting intensive research into a near-field recording (NFR) device based on the near-field optics, so that the NFR device can record or reproduce information smaller than the wavelength of the optical signal.
The NFR device including a near-field forming lens acquires an optical signal of less than a diffraction limitation using an improved near-field forming lens having a refractive index higher than that of an objective lens.
The optical signal is configured in the form of evanescent waves, and is then propagated to a recording medium adjacent to an interface or boundary, so that high-density bit information is stored in the recording medium. In this case, for the convenience of description, an area for forming evanescent waves is referred to as a near-field.
However, the above-mentioned conventional art has the following problems.
The above-mentioned optical recording/reproducing device based on the near-field cannot be compatible with conventional recording mediums.
In addition, the above-mentioned optical recording/reproducing device has difficulty in solving the collision problems caused by a tilt or vibration encountered while a desired short distance between the recording medium and the lens is maintained.